Adding UMA to track previews opt outs and blacklist eligibility

components/previews/core/previews_black_list.h

Index: components/previews/core/previews_black_list.h
diff --git a/components/previews/core/previews_black_list.h b/components/previews/core/previews_black_list.h
index ad192463f17372ea9b166b89fa643976b99d4584..cdc2e000e208c54132d78e40df7400e2b6e2fa88 100644
--- a/components/previews/core/previews_black_list.h
+++ b/components/previews/core/previews_black_list.h
@@ -23,20 +23,38 @@
 
 class GURL;
 
 namespace base {
 class Clock;
 }
 
 namespace previews {
 class PreviewsBlackListItem;
 
+enum class PreviewsEligibilityReason {

[tbansal1, 2016/11/08 00:30:52]

nit: Is there a reason to use this style of comments vs.
enum class A {
// comment for VALUE1
VALUE1 = 0,

// comment for VALUE2
...
};

I find the latter slightly more readable especially when the comment is
multi-line.

[RyanSturm, 2016/11/08 22:22:29]

Done.

+  ALLOWED = 0,                // The preview navigation was allowed.
+  BLACKLIST_UNAVAILABLE = 1,  // The black list was not initialized.
+  BLACKLIST_DATA_NOT_LOADED =
+      2,                        // The black list has not loaded from disk yet.
+  USER_RECENTLY_OPTED_OUT = 3,  // The user has opted out of a preview
+                                // recently.
+  USER_BLACKLISTED = 4,  // The user has opted out of previews often, and is no
+                         // longer shown previews on any host.
+  HOST_BLACKLISTED = 5,  // The user has opted out of previews on a specific
+                         // host often, and was not not shown a previews on that
+                         // host.
+  NETWORK_QUALITY_UNAVAILABLE =
+      6,                 // the network quality estimate is not available.
+  NETWORK_NOT_SLOW = 7,  // The network was fast enough to not warrant previews.
+  LAST = 8,
+};
+
 // Manages the state of black listed domains for the previews experiment. Loads
 // the stored black list from |opt_out_store| and manages an in memory black
 // list on the IO thread. Updates to the black list are stored in memory and
 // pushed to the store. Asynchronous modifications are stored in a queue and
 // executed in order. Reading from the black list is always synchronous, and if
 // the black list is not currently loaded (e.g., at startup, after clearing
 // browsing history), domains are reported as black listed. The list stores no
 // more than previews::params::MaxInMemoryHostsInBlackList hosts in-memory,
 // which defaults to 100.
 class PreviewsBlackList {
@@ -51,23 +69,24 @@ class PreviewsBlackList {
 
   // Asynchronously adds a new navigation to to the in-memory black list and
   // backing store. |opt_out| is whether the user opted out of the preview or
   // navigated away from the page without opting out. |type| is only passed to
   // the backing store. If the in memory map has reached the max number of hosts
   // allowed, and |url| is a new host, a host will be evicted based on recency
   // of the hosts most recent opt out.
   void AddPreviewNavigation(const GURL& url, bool opt_out, PreviewsType type);
 
   // Synchronously determines if |host_name| should be allowed to show previews.
-  // If the black list has loaded yet, this will always return false. |type| is
-  // not used to make this decision.
-  bool IsLoadedAndAllowed(const GURL& url, PreviewsType type) const;
+  // Returns the reason the blacklist disallowed the preview, or
+  // PreviewsEligibilityReason::ALLOWED if the preview is allowed.
+  PreviewsEligibilityReason IsLoadedAndAllowed(const GURL& url,
+                                               PreviewsType type) const;
 
   // Asynchronously deletes all entries in the in-memory black list. Informs
   // the backing store to delete entries between |begin_time| and |end_time|,
   // and reloads entries into memory from the backing store. If the embedder
   // passed in a null store, resets all history in the in-memory black list.
   void ClearBlackList(base::Time begin_time, base::Time end_time);
 
   // Returns a new PreviewsBlackListItem representing |host_name|. Adds the new
   // item to |black_list_item_map|.
   static PreviewsBlackListItem* GetOrCreateBlackListItemForMap(